The Spread of free-riding behavior in a social network

We study a model where agents, located in a social network, decide whether to exert effort or not in experimenting with a new technology (or acquiring a new skill, innovating, etc.). We assume that agents have strong incentives to free ride on their neighbors' effort decisions. In the static version of the model efforts are chosen simultaneously. In equilibrium, agents exerting effort are never connected with each other and all other agents are connected with at least one agent exerting effort. We propose a mean-field dynamics in which agents choose in each period the best response to the last period's decisions of their neighbors. We characterize the equilibrium of such a dynamics and show how the pattern of free riders in the network depends on properties of the connectivity distribution.

The Paralympic Village: a barrier-free city

Article describing the design standards and their use for Paralympic facilities. This article was published in the book entitled Olympic Villages: a hundred years of urban planning and shared experiences compiling the papers given at the 1997 International Symposium on International Chair in Olympism (IOC-UAB).

Encryption methods using formal power series rings

Recently there has been a great deal of work on noncommutative algebraic cryptography. This involves the use of noncommutative algebraic objects as the platforms for encryption systems. Most of this work, such as the Anshel-Anshel-Goldfeld scheme, the Ko-Lee scheme and the Baumslag-Fine-Xu Modular group scheme use nonabelian groups as the basic algebraic object. Some of these encryption methods have been successful and some have been broken. It has been suggested that at this point further pure group theoretic research, with an eye towards cryptographic applications, is necessary.In the present study we attempt to extend the class of noncommutative algebraic objects to be used in cryptography. In particular we explore several different methods to use a formal power series ring R && x1; :::; xn && in noncommuting variables x1; :::; xn as a base to develop cryptosystems. Although R can be any ring we have in mind formal power series rings over the rationals Q. We use in particular a result of Magnus that a finitely generated free group F has a faithful representation in a quotient of the formal power series ring in noncommuting variables.

Estudi i implementació d'un arxivat de dades per a les plataformes SAP Enterprise 4.7 x 200 d'una gran empresa

En aquest projecte s'ha implementat un sistema de data archiving amb SAP-IXOS per a una empresa després que aquesta demanés consell a la nostra consultora per reduir espai en la base de dades, ja que només els quedava lliure un 14% de l'ocupació total, i d'aquesta forma millorar el rendiment del sistema. S'ha realitzat un estudi de la base de dades, ocupació en Mb i creixement mensual de les dades en les taules. S'han parametritzat objectes d'arxivat, creat i definits repositoris de contingut, fitxers lògics i s'han programat reports addicionals per arxivar les dades correctament. El resultat ha estat reduir la base de dades en un 22% sent posible l'entrada de noves dades obtenint una resposta més àgil del sistema.

Model structures on the category of small double categories

In this paper we obtain several model structures on DblCat, the category of small double categories. Our model structures have three sources. We first transfer across a categorification-nerve adjunction. Secondly, we view double categories as internal categories in Cat and take as our weak equivalences various internal equivalences defined via Grothendieck topologies. Thirdly, DblCat inherits a model structure as a category of algebras over a 2-monad. Some of these model structures coincide and the different points of view give us further results about cofibrant replacements and cofi brant objects. As part of this program we give explicit descriptions and discuss properties of free double categories, quotient double categories, colimits of double categories, and several nerves and categorifications.

Brown representability does not come for free

"Vegeu el resum a l'inici del document del fitxer adjunt."

On the intersection of free subgroups in free products of groups

"Vegeu el resum a l'inici del document del fitxer adjunt."

Object recognition for autonomous objects: comparison of two approaches

Report for the scientific sojourn at the Swiss Federal Institute of Technology Zurich, Switzerland, between September and December 2007. In order to make robots useful assistants for our everyday life, the ability to learn and recognize objects is of essential importance. However, object recognition in real scenes is one of the most challenging problems in computer vision, as it is necessary to deal with difficulties. Furthermore, in mobile robotics a new challenge is added to the list: computational complexity. In a dynamic world, information about the objects in the scene can become obsolete before it is ready to be used if the detection algorithm is not fast enough. Two recent object recognition techniques have achieved notable results: the constellation approach proposed by Lowe and the bag of words approach proposed by Nistér and Stewénius. The Lowe constellation approach is the one currently being used in the robot localization project of the COGNIRON project. This report is divided in two main sections. The first section is devoted to briefly review the currently used object recognition system, the Lowe approach, and bring to light the drawbacks found for object recognition in the context of indoor mobile robot navigation. Additionally the proposed improvements for the algorithm are described. In the second section the alternative bag of words method is reviewed, as well as several experiments conducted to evaluate its performance with our own object databases. Furthermore, some modifications to the original algorithm to make it suitable for object detection in unsegmented images are proposed.

Free Mobility and Taste-Homogeneity of Jurisdiction Structures

We consider a population of agents distributed on the unit interval. Agents form jurisdictions in order to provide a public facility and share its costs equally. This creates an incentive to form large entities. Individuals also incur a transportation cost depending on their location and that of the facility which makes small jurisdictions advantageous. We consider a fairly general class of distributions of agents and generalize previous versions of this model by allowing for non-linear transportation costs. We show that, in general, jurisdictions are not necessarily homogeneous. However, they are if facilities are always intraterritory and transportation costs are superadditive. Superadditivity can be weakened to strictly increasing and strictly concave when agents are uniformly distributed. Keywords: Consecutiveness, stratification, local public goods, coalition formation, country formation. JEL Classification: C71 (Cooperative Games), D71 (Social Choice; Clubs; Committees; Associations), H73 (Interjurisdictional Differentials and Their Effects).

On uniform conjugators in torsion-free hyperbolic groups

"Vegeu el resum a l'inici del document del fitxer adjunt."

Measuring intergenerational earnings mobility in Spain: a selection-bias-free approach

This paper analyses intergenerational earnings mobility in Spain correcting for different selection biases. We address the co-residence selection problem by combining information from two samples and using the two-sample two-stage least square estimator. We find a small decrease in elasticity when we move to younger cohorts. Furthermore, we find a higher correlation in the case of daughters than in the case of sons; however, when we consider the employment selection in the case of daughters, by adopting a Heckman-type correction method, the diference between sons and daughters disappears. By decomposing the sources of earnings elasticity across generations, we find that the correlation between child's and father's occupation is the most important component. Finally, quantile regressions estimates show that the influence of the father's earnings is greater when we move to the lower tail of the offspring's earnings distribution, especially in the case of daughters' earnings.

Cognition, Resources, and Institutions in the Explanation of Attitudes to Free Trade

This article proposes a framework for the analysis of attitudes to foreign trade policies that challenges the traditional skill-endowment approach. The traditional approach assumes informed individuals who calculate the costs and benefits of alternative policies. We propose that individuals lack information and that their positions rest on economic vulnerability, as mediated through risk-aversion. We also stress the role of environmental signals and political endorsements in guiding individuals' views on trade policy. We test this alternative approach with a Spanish survey conducted in May 2009 and the ISSP survey conducted in 2003 in a large number of less developed and more developed countries. The Spanish data show that the population is largely uninformed and that their ideas about the consequences of free trade policy do not explain attitudes among different socio-demographic groups. Meanwhile, the ISSP data contradict important aspects of the traditional approach and are consistent with the alternative approach.

Bounding the residual finiteness of free groups

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Is the Spanish Inheritance and Gift Tax incompatible with the free movement of workers and capital?: The reasoned opinion of the EU Commission IP/10/513

The aim of my speech is answering to the question if the Spanish Inheritance and Gift Tax is incompatible with the free movement of workers and capital. We are going to pay special attention to the European Commission’s request to Spain to change its Inheritance and Gift Tax provisions for Non-Residents or Assets held abroad. In order to answer to the question mentioned above five points will be explained. At first place I am going to describe the infrengement procedure established in the Article 258 that the EU Commission can follow when a Member State doesn’t comply with Community Law. At second place, we are going to explain what is the content of the EU Commission delivered on 5th of may 2010 regarding the spanish Inheritance and Gift Tax. Then, we will analise what establishes the Community Law regarding the freedom of workers and capital and how they are understood by the EU Court of Justice in similar cases. Finally, we are going to provide possible amendments that Spain could undertake.